Measurement system comprising an acceleration sensor and a position sensor

ABSTRACT

A measurement system for determining acceleration and a position of an object. The measurement system includes a first sensor system for determining an acceleration of an object, the first sensor having a body with an electrically conducting measuring structure, a device for generating a first magnetic field, which acts on the measuring structure and a detector for detecting a second magnetic field or field changes, which are created by eddy currents generated by the measuring structure, the detector generating an output signal. A second sensor system for determining a position of the object, the second sensor system includes a scale graduation that lies opposite the detector and is scanned by the detector in a scanning area in which the measuring structure and the scale graduation are arranged placed on top of each other, or integrated into each other, and wherein the detector generates an acceleration signal and a position signal from a common scanning area. The measuring structure and the scale graduation are formed on a common body.

Applicant claims, under 35 U.S.C. §§120 and 365, the benefit of priorityof the filing date of Aug. 2, 2000 of a Patent Cooperation Treaty patentapplication, copy attached, Ser. No. PCT/EP00/07474, filed on theaforementioned date, the entire contents of which are incorporatedherein by reference, wherein Patent Cooperation Treaty patentapplication Ser. No. PCT/EP00/07474 was not published under PCT Article21(2) in English.

Applicant claims, under 35 U.S.C. §119, the benefit of priority of thefiling date of Sep. 30, 1999 of a German patent application, copyattached, Ser. No. 199 47 277.7, filed on the aforementioned date, theentire contents of which are incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a measurement system.

2. Description of the Related Art

A measurement system is described in EP 0 661 543 B1. It includes anacceleration sensor in the form of a Ferraris sensor, wherein a magneticflux passes vertically through an electrically conducting disk,constituting the measuring structure. This magnetic flux is generated bya magnet. If the disk is moved with respect to the magnet, eddy currentsare created, which in turn generate a magnetic field. The changes inthis magnetic field, or flux, are detected by a detector in the form ofa coil and are a measure for the acceleration. An optically orinductively scannable scale graduation is fixed on the edge of this diskand is scanned by a scanning head for determining the position of thisdisk.

SUMMARY AND OBJECTS OF THE INVENTION

It is therefore an object of the present invention to design ameasurement system with an acceleration sensor and a position sensor insuch a way that as compact a structure as possible is achieved.

This object is attained by a measurement system for determiningacceleration and a position of an object. The measurement systemincludes a first sensor system for determining an acceleration of anobject, the first sensor system having a body with an electricallyconducting measuring structure, a device for generating a first magneticfield, which acts on the measuring structure and a detector fordetecting a second magnetic field or field changes, which are created byeddy currents generated by the measuring structure, the detectorgenerating an output signal. A second sensor system for determining aposition of the object, the second sensor system includes a scalegraduation that lies opposite the detector and is scanned by thedetector in a scanning area in which the measuring structure and thescale graduation are arranged placed on top of each other, or integratedinto each other, and wherein the detector generates an accelerationsignal and a position signal from a common scanning area. The measuringstructure and the scale graduation are formed on a common body.

The measurement system of the present invention has the advantage thatthe scale graduation required for the position measurement is provideddirectly on the measuring structure for the acceleration measurement andis therefore arranged in a space-saving manner. The acceleration signaland the position signal are here derived from a common scanning area. Itis realized that no scanning areas which are located transversely withrespect to the measuring direction are required.

Advantageously the electrical properties of the measuring structure ofthe acceleration sensor are not affected by the scale graduation. Thescale graduation of the acceleration sensor can be realized in aseparate layer, or in a layer package, which is connected with themeasuring structure of the acceleration sensor in such a way that themeasuring structure can expand independently of the layers supportingthe scale graduation.

It is alternatively possible to embody the scale graduation in themeasuring structure itself, wherein it is then necessary to makeprovisions, such as signal filtering, signal smoothing, multiplexing, orswitching between several detectors, or averaging, in order to keep theacceleration signal as unaffected as possible by the measuringrepresentation.

The present invention will be explained in greater detail in whatfollows by the drawings. Shown are in:

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 schematically shows a perspective view of a first exemplaryembodiment of a measurement system in accordance with the presentinvention;

FIG. 2 shows a perspective view of a second exemplary embodiment of asensor system in accordance with the present invention to be used withthe measurement system of FIG. 1;

FIG. 3 schematically shows a top view of a second exemplary embodimentof a measurement system in accordance with the present invention;

FIG. 4 shows a perspective plan view of a second exemplary embodiment ofa measuring structure in accordance with the present invention to beused with the measurement system of FIG. 3; and

FIG. 5 shows a perspective view of a third exemplary embodiment of asensor system in accordance with the present invention to be used withthe measurement systems of FIGS. 1 and 3.

DESCRIPTION OF THE PREFERRED EMBODIMENT(S) OF THE INVENTION

The measurement system in accordance with FIG. 1 includes a disk 1 madeof an electrically conducting material, on whose surface a scalegraduation in the form of an incremental scale graduation 2, which canbe photoelectrically scanned, has been embodied. For this purpose thedisk 1 itself can be structured on its surface in that, for example,depressions are partially cut in the circumferential direction (movementdirection X), wherein the alternatingly arranged depressions andelevations form a phase grating, known per se.

However, the graduation 2 can also be embodied as a separate layer, oras a layered package, on the disk 2, this embodiment is shown in dashedlines of FIG. 1.

A sensor system for measuring acceleration of disk 1 includes magnet 3,disk 1 and coil 4. In particular, a magnet 3, or a coil for generating amagnetic field Φ1, which acts on the disk 1 vertically with respect tothe movement direction X, is provided for measuring the acceleration ofthe disk 1 in the movement direction X (rotation). The magnetic field Φ1creates eddy currents in the disk 1, which are proportional to themovement speed of the disk 1. These eddy currents create a furthermagnetic field Φ2, which is detected by a coil 4. The voltage Ugenerated in the coil 4 is proportional to the acceleration of the disk1. This principle of acceleration measurement is also known as theFerraris principle.

A sensor system for measuring a position of disk 1 includes disk 1,scanning head 5 and graduation 2. In accordance with the presentinvention, the position signal P for the position measurement isobtained from the same area of the disk 1 from which the acceleration Uis derived. A scanning head 5 is assigned to the graduation 2 for thispurpose, which in a known manner contains a light source and aphotosensitive cell. The light from the light source is directed ontothe graduation 2, is modulated there as a function of the position andis reflected toward the photosensitive cell.

If the graduation 2 is an integral part of the disk 1, or if thegraduation 2 has a layer of electrically conductive material, eddycurrents are also created in the graduation 2 as a rule. This can affectthe acceleration measurement in an undesirable way. To prevent eddycurrents in the graduation 2, a value is selected for the graduationperiod T so that they cannot flow. In the course of this, use is made ofthe fact that eddy currents have a defined spatial extension, which isnot present in a graduation 2 of an appropriately fine graduation periodT, in particular less than 0.3 mm. It is possible in this way toeffectively prevent eddy currents, which could alter the result of theacceleration measurement, from being induced in the area of thegraduation 2, even though it is made of a conductive material.

If the graduation 2 is exclusively of an electrically non-conductingmaterial, the graduation 2 does not affect the acceleration measurement.In this case the graduation 2 can be a known phase grating, made ofareas of different refractive indices and/or step heights, which arealternatingly arranged in the measuring direction X.

If the graduation 2 contains electrically conducting material, and ifthe graduation period is not selected to be so fine that eddy currentscannot be created at all, there is the possibility of selecting theactive detection surface of the coil 4 to be sufficiently large, so thatthe magnetic field Φ2 detected by the magnetic coil 4 is averaged overmany graduation periods P. Because of this, only negligible fluctuationsin the detected acceleration signal U are caused by the graduation 2. Inorder to provide integration of as many graduation periods P aspossible, the coil 4 can be designed in such a way that the activesurface through which the flux Φ2 generated by the eddy current passesdescribes at least approximately a whole circle of 360. A parallel orseries connection of several smaller coils is alternatively alsoconceivable. In this case it is advantageous to produce the coil, or thecoils, by thin film technology. Then the support for the coils cansimultaneously be the support for the elements of the scanning head forposition measuring.

Alternatively to this there is the option that the position informationP is contained in the acceleration signal U, and these high-frequencysignal portions are separated from the low-frequency signal portion ofthe acceleration signal U by a high-pass filter. A counter is thentriggered by the output signal of the high-pass filter which countsposition changes in multiples of the graduation period T. The position,as well as the acceleration, are determined by evaluating the outputsignal U of the coil 4.

If the graduation 2 is embodied as a separate layer, or as a layerpackage, on the disk 1, it is advantageous if the connection of thegraduation 2 with the disk 1 permits a temperature-related expansion ofthe disk 1 in relation to the graduation layer 2 without animpermissible force being exerted on the graduation layer 2, so that nodeformation, or even destruction, of the graduation layer because of anexpansion of the disk 1 results.

The graduation 2 can also be embodied so it can be scanned capacitively,inductively or magnetically.

The measuring structure for acceleration measurement need not beembodied as a disk 1, it can also be applied as a layer 6 made of anelectrically conducting material on an insulating support 7, for examplemade of glass, plastic or printed circuit board material. The graduation2 can be embodied on this support 7 on the layer 6 in the form of astepped reflecting phase graduation, or in the form of an amplitudegrating produced in accordance with known lithographic methods. Thisembodiment is schematically represented in FIG. 2.

How conducting areas 2.1 of an absolute graduation can be used as ameasuring structure for acceleration measurement at the same time isdescribed in a further exemplary embodiment in accordance with FIGS. 3and 4. FIG. 3 shows a view from above on a known absolute graduation 2which, in accordance with the present invention, is scanned fordetermining a position, as well as by the acceleration sensors 4. FIG. 4represents a perspective view of the graduation 2 in FIG. 3.Electrically conducting areas 2.1 are distributed on a rotating,non-conducting support 7, so that the conducting areas 2.1 form anabsolute coded graduation 2. In accordance with FIG. 3, the accelerationsensors 4 are arranged in such a way that at least one accelerationsensor 4 is always above a conducting area 2.1. Because of a constantmagnetic flux Φ1 vertically with respect to the surface of thegraduation 2, which is generated by a device not represented here,changing eddy currents are caused in the conducting areas 2.1 in case ofan accelerated movement of the graduation 2. In the simplest case thedevice for generating a constant magnetic flux Φ1 is a permanent magnet.The eddy currents, which change with an accelerated movement, cause amagnetic flux Φ2 themselves, which is detected by the accelerationsensors in the form of several coils 4.

In this case the acceleration sensors 4 must be arranged, or it isnecessary to arrange as many acceleration sensors 4 in such a way thatduring the rotation at least one acceleration sensor 4 is always over aconducting area 2.1. Moreover, eddy currents at the edge of theconducting area 2.1 should not be detected, because there the eddycurrents are affected by the border of the conducting area 2.1, so thatit is advantageous to arrange at least three acceleration sensors. Bythis it is possible to assure that a change of the eddy current fieldbecause of an acceleration can always be detected by at least one of theacceleration sensors 4.

In accordance with the shape of the conducting areas 2.1 above which theacceleration sensors 4 are arranged, the arrangement of the accelerationsensors 4, the detected position and direction of rotation, the outputsignal of the respective acceleration sensor 4 which at that time islocated over a conducting area 2.1 is passed on for evaluation by aswitching device 8. It is possible here to implement the switchingdevice 8 as a multiplexer known from the prior art, for which thecontrol signals S for switching are detected in a control unit 9 fromthe shape of the conducting areas 2.1 above which the accelerationsensors 4 are arranged, the arrangement of the acceleration sensors 4,the detected position and direction of rotation. Switching of theconfiguration includes acceleration sensors 4 and conducting areas 2.1of an absolute graduation 2 represented in FIG. 3 from one accelerationsensor 4 to the next takes place in the order of their arrangement in aclockwise or counterclockwise direction after a rotation of thegraduation 2 over 120.

In a further embodiment, the conducting areas 2.1 of the absolutegraduation 2 can be provided on both sides of the graduation support 7.In that case the top and underside are scanned by acceleration sensors4. This has the advantage that it is possible by an appropriateswitching of the output signals from the acceleration sensors 4 tocompensate fluctuating distances between the acceleration sensors 4 andthe conducting areas 2.1. When the distance between the accelerationsensors 4 and the conducting areas 2.1 on the top increases, thisdistance decreases on the underside, and vice versa. This is used forcompensating the amplitude fluctuations of the output signals of theacceleration sensors 4.

The exemplary embodiments so far are related to rotary measurementsystems. The teaching regarding technical processes recited in theseexemplary embodiments can also be identically employed with linearmeasuring systems, the same as the teaching regarding technicalprocesses in the following exemplary embodiment of a linear measurementsystem can be employed in a manner identical to that of a rotarymeasurement system.

In the exemplary embodiment of FIG. 5, a graduation structure 2 of alinear measurement system is directly integrated in a measuringstructure 1 for the acceleration sensor. This takes place in that themeasuring structure is designed to be electrically homogeneous andoptically inhomogeneous.

For this purpose, a ribbon-shaped electrical conductor 1 is provided asthe measuring structure 1 for the acceleration sensor, whose surfacefacing the scanning head 5 only slightly reflects light. Subsequentlythe surface of the ribbon-shaped conductor 1 is processed in such a waythat, corresponding to the desired graduation period of the positionsensor, light is well reflected in the processed areas. The reverse caseis of course also possible, that light is well reflected by theribbon-shaped electrical conductor 1 and, following processing, is onlybadly reflected in the processed areas.

Because processed and non-processed areas of the graduation period Talternate, it is possible to implement an incremental or absolutegraduation 2, which can be used for a position measurement based on theoptical scanning principle. Since only the optical properties of theribbon-shaped conductor 1 are changed, its electrical conductivity isnot change by the graduation 2, and therefore eddy currents foracceleration measurement are not affected by the graduation 2 forposition measurement.

Processing of areas for making them more or less reflective can beperformed in several different ways. For example, a thin non-conductingmarking can be applied, or an already provided thin non-conductingmarking can be removed. Here, the thin, non-conducting marking and theelectrical conductor 1 should have different optical properties, bywhich a graduation 2 for optical scanning is provided.

Further possibilities for providing the electrical conductor 1 with anoptical, inductive, magnetic or capacitive graduation 2 without changingthe electrical resistance include changing the structure of the materialto correspond to the graduation period T. Furthermore, the structure ofthe electrical conductor 1 can be partially changed by conversion ordoping in order to obtain a graduation 2 without changing the electricalproperties.

Alternatively to that there is also the possibility of removing materialfrom the measuring structure 1 at places at which markings for aposition measurement are intended. This can take place by an etchingprocess, for example. By this the conductivity is reduced at theselocations, which can be undesirable. To compensate for this, materialwith optical properties which are different in comparison with thematerial of the measuring structure 1 is deposited at these locations.Here, the amount of the deposited material is selected as a function ofthe conductivity of this material, so that the measuring structure 1 forthe acceleration measurement again has the same electrical conductivityat each location.

The invention may be embodied in other forms than those specificallydisclosed herein without departing from its spirit or essentialcharacteristics. The described embodiments are to be considered in allrespects only as illustrative and not restrictive, and the scope of theinvention is commensurate with the appended claims rather than theforegoing description.

I claim:
 1. A measurement system for determining acceleration and aposition of an object, comprising: a first sensor system for determiningan acceleration of an object, said first sensor system comprising: abody with an electrically conducting measuring structure; a device forgenerating a first magnetic field, which acts on said measuringstructure; and a detector for detecting a second magnetic field or fieldchanges, which are created by eddy currents generated by said measuringstructure, said detector generating an output signal; a second sensorsystem for determining a position of said object, said second sensorsystem comprises a scale graduation that lies opposite said detector andis scanned by said detector in a scanning area in which said measuringstructure and said scale graduation are arranged placed on top of eachother, or integrated into each other, and wherein said detectorgenerates an acceleration signal and a position signal from a commonscanning area; and said measuring structure and said scale graduationare formed on a common body.
 2. The measurement system in accordancewith claim 1, wherein said scale graduation comprises electricallyconducting areas.
 3. The measurement system in accordance with claim 1,wherein said measuring structure is structured in such a way that saidsecond magnetic field varies as a function of a position in a movementdirection of said body.
 4. The measurement system in accordance withclaim 2, wherein said measuring structure is structured in such a waythat said second magnetic field varies as a function of a position in amovement direction of said body.
 5. The measurement system in accordancewith claim 1, wherein said acceleration signal is superimposed on saidposition signal.
 6. The measurement system in accordance with claim 4,wherein said acceleration signal is superimposed on said positionsignal.
 7. The measurement system in accordance with claim 1, furthercomprising: a filter that receives said acceleration signal and selectshigh-frequency signals; and high-frequency components that generate saidposition signal.
 8. The measurement system in accordance with claim 1,further comprising: a second detector that generates a second outputsignal; a switching device that selects either said output signal orsaid second output signal as said acceleration signal.
 9. Themeasurement system in accordance with claim 8, where said scalegraduation comprises a partially electrically conducting area.
 10. Themeasurement system in accordance with claim 2, wherein said scalegraduation comprises a layer or a layer package which is applied on saidelectrically conducting areas.
 11. The measurement system in accordancewith claim 10, wherein said measuring structure comprises a layer or alayer package of electrically conducting material on an electricallynon-conducting support.
 12. A measurement system for determiningacceleration and a position of an object, comprising: a first sensorsystem for determining an acceleration of an object, said first sensorsystem comprising: a body with an electrically conducting measuringstructure; a device for generating a first magnetic field, which acts onsaid measuring structure; and a first detector for detecting a secondmagnetic field or field changes, which are created by eddy currentsgenerated by said measuring structure, said first detector generating anoutput signal; a second sensor system for determining a position of saidobject, said second sensor system comprises a scale graduation that liesopposite said first detector and is scanned by a position detector in ascanning area in which said measuring structure and said scalegraduation are arranged placed on top of each other, or integrated intoeach other, and wherein said first detector generates an accelerationsignal and said position detector generates a position signal from acommon scanning area; and said measuring structure and said scalegraduation are formed on a common body.
 13. The measurement system inaccordance with claim 12, wherein said scale graduation compriseselectrically conducting areas.
 14. The measurement system in accordancewith claim 12, wherein said measuring structure is structured in such away that said second magnetic field varies as a function of a positionin a movement direction of said body.
 15. The measurement system inaccordance with claim 13, wherein said measuring structure is structuredin such a way that said second magnetic field varies as a function of aposition in a movement direction of said body.
 16. The measurementsystem in accordance with claim 12, further comprising: a seconddetector that generates a second output signal; a switching device thatselects either said output signal or said second output signal as saidacceleration signal.
 17. The measurement system in accordance with claim16, where said scale graduation comprises a partially electricallyconducting area.
 18. The measurement system in accordance with claim 17,wherein said scale graduation comprises a layer or a layer package whichis applied on said partially electrically conducting area.
 19. Themeasurement system in accordance with claim 12, wherein said scalegraduation is embodied to reflect light and comprises elevations anddepressions which are alternatingly arranged in a movement direction ofsaid body.
 20. The measurement system in accordance with claim 19,wherein said elevations comprise electrically conducting areas, whosedimensions are selected to be so small that no eddy currents arecreated.
 21. The measurement system in accordance with claim 12, whereinsaid scale graduation is structured to be photoelectrically scannableand wherein said detector comprises an optical scanning head forscanning said scale graduation.
 22. The measurement system in accordancewith claim 13, wherein said scale graduation comprises a layer or alayer package which is applied on said electrically conducting areas.23. The measurement system in accordance with claim 22, wherein saidmeasuring structure comprises a layer or a layer package of electricallyconducting material on an electrically non-conducting support.